Electric furnace



April 1935- A. s. LOBLEY I 1,996,680

ELECTRIC FURNACE Filed Jan. 4, 1933 Patented Apr. 2, 1935 Alfred Glynne Lobley, England, assignor of Erdington, Birmingham, one-half to Birmingham Electric Furnaces, Limited, Erdlngton, Birmingham, England, a

Application January 4,

British company 1933, Serial No. 650,183

In Great Britain January 26, 1932 4. Claims.

This invention has reference to electric furnaces for tempering or annealing metal products and performing similar heat-treatment operations at relatively low temperatures, and consists in or comprises certain improvements, as

hereinafter described, in resistance furnaces of the type wherein the treatment heat is conveyed from the electric resistance units or heating elements to the work-charge by fan-circulated aircurrents.

It has long been common practice in furnaces where the treatment or work-containing chamber also houses the resistance units, to provide within the said chamber, an open or un-cased propellortype fan to beat-up the air, or to promote a circulation of air over the work and thus assist the transference of heat to the latter from the resistors.

It has also been proposed (as for example in British Specification No. 247,912) to use a reversiblepropeller-type fan which operates in a relatively small orifice at one end of a treatment chamber whose other end is open to allow for the introduction of work; the said orifice and opening both having communication with an annular chamber which surrounds the treatment chamber and houses the resistor units. In this furnace, the heat-transferring air-circulation is periodically reversed by reversing the direction of rotation of the fan.

Further, in British Specification No. 334,621 of 1929, it has been proposed to use, in a furnace wherein the treatment chamber or oven also houses the resistance units, an open or un-cased internal fan of the centrifugal type whereby the air within the oven is collected by the fan axially and is projected horizontally outwards against the walls of the oven.

And in the specification of British Letters Patent No. 343,529 of 1929 I describe and illustrate furnaces having a resistance chamber outside the treatment chamber and provided with an enclosed or encased centrifugal fan operating to extract air from below the work-containing region of the treatment chamber and to force the said air through the resistance chamber and thence into the treatment chamber through an intake orifice of relatively small area located .above the said work-containing region.

The furnaces described in said British Specification No. 343,529 are, however, of the"horizontal type 'where the charging, door or aperture is located at one side of the furnace structure, and makes it impossible to use a system of resistors that entirely surrounds the treatment chamber.

Further, the small area air-intake orifice of the treatment chamber tends to obstruct the circulation of air in the system and prevents the useful employment of a fan capable of circulating a relatively large volume of air at that high velocity which has since been found to be essential to the rapid and uniform heating of the work.

According to the present invention, and in order to enable the advantageous use of a power ful or high-velocity centrifugal fan in conjunc- 10 tion with an emcient system of resistor elements having a high heat-input capacity, the furnace structure comprises a treatment chamber or oven having a charging-opening communicating with a resistance-housing chamber'which surrounds the 1 said treatment chamber,- and an air-extraction orifice which opens into, or constitutes the eye of, a voluted casing wherein the fan operates;

. the said fan-casing being adapted to discharge the air into a region of the resistance chamber 20 remote from that where the air is re-delivered to the oven after having travelled over the external resistors. This construction makes effective use of the known higher efliciency of a volute-cased centrifugal fan as compared with that of an open or un-cased centrifugal fan.

Provision is made for supporting the work charges in the region of the oven intermediate the air-intake and the air-extraction orifice, Whilst to assist or ensure a cyclonic movement 30 of the fan-impelled air, a system of director baffles may be so located between the resistor chamber and the oven that the resistor-heated air is delivered into the said oven in a series of streams or currents that impinge tangentially, 35

or cyclonically, upon the work charge;

The accompanying drawing represents, diagrammatically, a vertical or top-charging tempering furnace constructed in accordance with one application of the present invention. 0

Figure 1 being a vertical section of the structure.

Figure 2 a. horizontal section on the dotted line 2-2, and

Figure 3 another horizontal section on the dotted line 3-3.

In this furnace, the cylindrical treatment chamber or oven a has an open top or mouth a wherethrough a charge-containing basket may be passed or lowered and raised when the lid or cover b is removed. This top opening or charging orifice also constitutes the air-intake of the forced circulation system'and is indirect communication with the open upper end of an annular chamber e which surrounds the treatment chamber and in which a system of resistor units e is installed; these units being external to the oven whose walls a serve to direct the circulating air over the said resistors.

An air-extraction orifice c is formedin the bottom wall of the said oven, and below this is located a voluted fan-casing d in which a centrifugal fan d is housed and operates. The

orifice c constitutes, in effect, the intake eye of the fan-casing whose outlets d are arranged to discharge the fan-impelled air upwardly into the resistance chamber, or into a region of the saidchamber remote from the charging mouth a wherethrough the air is re-delivered into the top of the oven after having been forced over the external resistors.

To provide for a tangential direction oi. air into the top of the oven, or to ensure a cyclonic or eddying movement of air within the said chamber, the space immediately above the airdelivery end of the resistor-chamber is provided with a system of bailles J; these baifles being of a tangential or voluted form or disposition so that. they constrain the fan-propelled airstreams passing between them to enter the oven.

tangentially, or in a manner that ensures the desired cyclonic or eddying travel of the air in its passage through the said chamber, and over or in contact with the work charge, to the air-extraction orifice c In the construction shown, the baflles or air-directors are mounted on an internal wall of the structure immediately above the outlet or air-delivery ends of the reparticularly advantageous from the point of view of eificiency and, where a large and powerful fan is employed, enables the attainment of a high-speed air circulation and a uniform temperature distribution, with a smaller temperature gradient as the air passes through the work charge.

' In the furnaces above described, it is possible accurately to follow and observe the process of heat absorption in the work charge by arranging thermo-couples or pyrometers at the air delivery and aii'extra ction sides of the treatment chamber and noting the temperature differences at these points; the recording of substantially the same temperature by both instruments being an indication that the charge is no longer absorbing heat and that the treatment is finished. The temperature differences can be shown graphically by a recording instrument, or merely by an indicating instrument; or the instruments can be made to operate an audible or visible signal (such as a lamp or bell) when the treatment is finished.

Having described my invention what I claim and desire to secure by Letters Patent is:-

1. An electric furnace comprising an outer casing having a charging opening through one wall thereof, means for normally closing said opening, a treatment chamber within said casing having an air inlet and an air outlet at its opposite ends and having its side walls spaced from the inner walls of the casing to form a surrounding chamber communicating with the air inlet and air outlet of the treatment chamber, resistor units within said surrounding chamber, a volute fan casing within said outer casing having an intake communicating with the air outlet of the treatment chamber and a voluted outlet in direct communication with the surrounding chamber, a

centrifugal fan within said volute casing, and

means to drive said fan to draw the air through the treatment chamber and to force the same through the voluted outlet of the fan casing,

of the treatment chamber, said baflles being tan-' gentially disposed with respect to the inlet of the treatment chamber to cause the air entering the said inlet to enter the treatment chamber tangentially to insure the desired cyclonic or eddying travel of the air during its passage through said chamber.

3. An electric furnace comprising an outer casing having a charging opening through the top wall thereof, means for normally closing said opening, a treatment chamber within said casing having an air inlet spaced from the top of the casing and an air outlet spaced from the bottom of said casing, the side walls of the treatment chamber being spaced from the inner walls of the casing to form a surrounding chamber communicating with the air inlet and air outlet of the treatment chamber, resistor units within said surrounding chamber, a volute fan casing mounted within the outer casing at the bottom thereof and having an intake communicating with the air outlet of the treatment chamber and having a voluted outlet in direct communication with the lower portion of the surrounding chamber, a centrifugal fan within said volute casing, and means to drive said fan to draw air downwardly through the treatment chamber into the volute fan casing and to force the air from the fan casing through the voluted outlet of the fan casing, and spirally through the surrounding chamber toward the top thereof and past the resistor units therein and into the air inlet opening in the upper end of the treatment chamber.

4. An electric furnace as claimed in claim 3, including baflles positioned between the air inlet at the top of the treatment chamber and the upper end of the communicating surrounding chamber, said bafiles being tangentially disposed with ,respect to the inlet of the treatment chamber to cause the air passing through said inlet to enter the upper end of the treatment chamber to insure the desired cyclonic or eddying travel of the air during its passage through said chamber.

ALFRED GLYNNE LOBLEY. 

